According to a first aspect of the invention, there is provided a process for treating unsaturated hydrocarbons, which process comprises subjecting an unsaturated hydrocarbon component to metathesis in the presence of a catalyst system comprising silica, alumina and an alkyl tin compound, thereby to form one or more different hydrocarbons.
In principle, any unsaturated hydrocarbons can be treated in the process of the invention. However, the unsaturated hydrocarbon component may particularly comprise an internal olefin, such as 2-octene; an external olefin, such as 1-octene; or an unsaturated cyclic hydrocarbon, such as norbornene.
The metathesis reaction which takes place in the presence of the catalyst system involves breaking carbon-carbon double bonds and rearranging the resultant radicals to form the different or more desired hydrocarbons, which are usually also unsaturated. When an olefin hydrocarbon is used as feedstock, the following generalized metathesis reaction can take place: EQU 2R'HC.dbd.CHR".revreaction.R'HC.dbd.CHR'+R"HC.dbd.CHR"
where R' and R" represent hydrocarbon radicals.
The more desired hydrocarbons which are formed are dependent primarily on the particular unsaturated hydrocarbon used as feedstock. Thus, if 1-octene is used as feedstock, the more desired hydrocarbons formed are primarily 7-tetradecene and ethene.
When an unsaturated cyclic hydrocarbon is used as feedstock, then the metathesis reaction usually involves ring opening polymerization.
The catalyst system may comprise a silica-alumina compound or substance as a first component, with the alkyl tin compound admixed therewith as a second component.
The first component thus comprises a silica-alumina compound or substance having the formula SiO.sub.2.Al.sub.2 O.sub.3. The proportion of SiO.sub.2 to Al.sub.2 O.sub.3 therein can vary, but it is believed that when the molar ratio of SiO.sub.2 :Al.sub.2 O.sub.3 in the first component of the catalyst system is between 77:23 and 75:25, good results will be obtained, due to the strong acidic nature thereof.
The first component is preferably activated thermally before the second component is admixed therewith. This may be effected by treating the first component with oxygen at elevated temperature, eg at about 500.degree. C., for a period of time, eg about 3 hours, and thereafter with nitrogen, also at elevated temperature, eg at about 500.degree. C., for a period of time, eg about 2 hours.
To enhance the activity and/or the selectivity of the resultant catalyst system, the first component may, before the thermal activation thereof, be treated, eg impregnated, with phosphate ions and/or with cesium ions.
The admixing of the second component with the first component may be effected at room temperature.
The second component thus has the formula SnR.sub.4, where R is an alkyl group. In particular, R may be methyl, ie Me.
The proportion of SnMe.sub.4 to SiO.sub.2.Al.sub.2 O.sub.3 may be about 5,5.times.10.sup.-5 mol SnMe.sub.4 /1g SiO.sub.2.Al.sub.2 O.sub.3 in the case where the first component is not pretreated with ions as hereinbefore described. When the first component contains 2% (mass basis) phosphate (PO.sub.4.sup.3-) ions, then the proportion of SnMe.sub.4 to SiO.sub.2.Al.sub.2 O.sub.3 may be about 6,2.times.10-5 mol SnMe.sub.4 /1g SiO.sub.2.Al.sub.2 O.sub.3.
The catalyst system preferably contains no transition metal, eg contains no tungsten, molybdenum or rhenium.
The metathesis may be effected at room temperature and at about atmospheric pressure.
According to a second aspect of the invention, there is provided a catalyst system suitable for use in the metathesis of unsaturated hydrocarbons, the catalyst system comprising silica, alumina and an alkyl tin compound in intimate contact with one another.
The catalyst system may thus be as hereinbefore described.
According to a third aspect of the invention, there is provided a method of making a catalyst system suitable for use in the metathesis of unsaturated hydrocarbons, the method comprising admixing a silica-alumina compound with an alkyl tin compound, to obtain a catalyst system comprising silica, alumina and an alkyl tin compound.
The method of making the catalyst system may thus be as hereinbefore described.